1. Field of the Invention
The present invention relates to a printing press and more particularly a structure of a printing section disposed between a sheet feeding section and a sheet discharge section so as to supply a printing plate to a clamping gripper that is mounted on a plate cylinder and mount the same on the plate cylinder.
2. Related Art
A sheet-fed printing press (hereinafter referred simply to a printing press) generally includes a printing section between a sheet feeding section and a sheet discharge section. This printing section is to print on sheets by a printing plate mounted on a plate cylinder mounted inside of a body cover. The printing press is generally equipped with a printing plate mounting device that automatically mounts a printing plate, which has been manually inserted into a clamping gripper mounted on the plate cylinder. According to a recently proposed printing press, an automatic supply mechanism is employed to automatically supply a printing plate (a new plate), which has been once set at a predetermined position by an operator, to a clamping gripper.
Also, there is proposed another type of a printing press equipped with a guide device that guides a printing plate, which has been released from a clamping gripper, to a plate discharge device both in plate supply and discharge operations. For example, Japanese Patent Application Laid-open No. Hei-07-290690 proposes a guide device, in which a plate supply roller and a plate discharge roller are eccentrically mounted in pair on a shaft so as to rotate the plate supply roller around the support shaft, thereby forming a plate supply passage in a plate supply operation by a plate supply device, and rotate the plate discharge roller around the support shaft, thereby forming a plate discharge passage in a plate discharge operation by a plate discharge device.
The changing of the rollers to be used respectively for the plate supply and discharge operations is necessary due to the use of ink, solvent and the like in a printing operation. That is, it is necessary to avoid a problem associated with a case where the same roller is used both in the plate supply and discharge operations, that is, a problem that the roller with ink attached thereto during the plate discharge operation must be used for guiding a printing plate to be supplied.
According to the shifting operation in the above printing press to select whether the plate supply roller or the plate discharge roller is to be used for guiding a printing plate, a friction roller separately provided from the plate supply roller and the plate discharge roller is brought into contact with a plate cylinder, and the shifting is made according to the rotational amount of this friction roller, so that the plate supply roller is moved closer to the clamping gripper in the plate supply operation and the plate discharge roller is moved closer to the clamping gripper in the plate discharge device.
For the selection of the roller for use by the contact of the friction roller with the plate cylinder in the above conventional guide device of the printing press, a possibility of slippage of the friction roller on the plate cylinder must be taken into account. Such slippage may deteriorate the reliability of the plate discharge device as the time of use of the plate discharge device elapses.
It is an object of the present invention to provide a printing press that is capable of guiding a printing plate, which is held in clamped relationship with the clamping gripper, so as to allow the same to be mounted on the plate cylinder with accuracy, while guiding a printing plate in the plate discharge direction with accuracy, as well as maintains the reliability for a long time.